X-ray imagers (e.g., x-ray detectors) may be fabricated in many ways, and may serve many purposes. Imagers with a collector layer or array of detector elements are, for example, used in Computed Tomography (CT) scanners. Imagers know as “flat panel imagers” are increasingly used in the field of medical diagnostics, as universal imager components which can be employed in different application-specific X-ray devices.
Two types of flat panel imagers are “direct conversion” and “indirect conversion”. In a direct conversion imager, an X-ray sensitive photoconductor is used to convert the X-rays directly into electrons. Since the photoconductor has low self-capacitance, charge collection capacitors can be fabricated by thin film techniques to act as a charge storage devices. In an indirect conversion imager, a scintillation layer above the light collector layer converts incident X-rays into photons of visible light that can then be converted into electrical signals by an array of light detector elements in the collector layer. Thus, an indirect converter has a scintillator of material in which incident X-radiation is converted into photons of visible light which can then be detected by an array of photosensors of the collector layer, disposed below the scintillator. Above and below the scintillator, there may be layers of a variety of materials. Some of the layers are used for protection, others are glue for mechanical support and others are for optical matching between light transferring surfaces of the layers. Optimally, light created by the scintillator would travel to the photodetector directly below where the light was created. However, as the scintillator emits the light into all directions (including “scattering” laterally within the layers), only a portion of the created photons will reach the photosensors directly below where the light was created.
Moreover, in some indirect imagers, a loss of light that is led away from the photosensors is avoided by a reflector or reflective layer, which is arranged above the scintillation layer and reflects the created light photons back into the scintillator and towards the photosensors. In this way the light yield, and with it the sensitivity and the signal-to-noise ratio of the imager can be increased. However, since the reflected light continues to scatter (including laterally within the layers), only a portion of this reflected light will reach the photosensors directly below where the light was created.
Thus, with indirect conversion there are negative influences on image sharpness (e.g., resolution) due to lateral light scatter in layers between the scintillator and the photosensors. In addition, there are also negative influences of the reflector on image sharpness due to the additional scattering of reflected photons in the imager layers (e.g., other than the scintillator) between the reflector and the collector's photosensors.